1. Field of the Invention
The present invention relates to electrical connectors, and more particularly relates to a two wire termination connection strip.
2. Description of the Prior Art
Many types of electrical connectors are known. In the field of telephony, one common type of connector assembly is the so-called connector block. Such blocks provide an interface, for example, between the internal telephone wires in a building structure and the external wires in an underground cable. Exemplary connector block assemblies are disclosed in U.S. Pat. No. 5,160,273 to Carney and U.S. Pat. No. 5,356,309 to Carney et al. The disclosure of both of these patents is expressly incorporated herein by reference.
Reference should be had to FIGS. 1 and 2, which are adapted from FIGS. 1 and 7 respectively of the Carney '273 patent. As shown therein, a prior art connector block 10 includes a contact holder portion 12 and a base portion 14. Contact holder portion 12 is formed with a plurality of slots 16, each of which has a wide portion 18 and a narrow portion 20. The wide portion 18 can receive and guide a wire into the narrow portion 20, which is preferably dimensioned to be less than the overall diameter of an insulated wire to be connected, yet greater than the diameter of the conductor portion of the wire. Thus, narrow portion 20 functions as a strain relief Contact holder 12 is formed with a plurality of internal cavities 22 for receiving insulation displacement contacts. Insulation displacement contacts 24 are inserted in cavities 22; the tails 26 of contacts 24 which are present in opposed cavities 22 touch and provide electrical contact.
Recently, it has become advantageous to be able to secure two wires in each slot 16, and thus in each insulation displacement contact 24. Such connections are desirable, for example, when installing additional equipment or extensions, and for other reasons known to those of skill in the art.
There are significant problems associated with attempting to secure two wires in prior art insulation displacement contacts, using prior art connector blocks. Reference should now be had to FIGS. 3A-3C which depict an insulation displacement contact 24 according to the prior art. The views are, respectively, a front, right side and rear view. FIGS. 3A and 3B depict the prior art insulation displacement contact 24 attached by its tail 26 to a forming strip 28, which is of use in manufacturing. Prior art contact 24 includes a V-groove 30 in both front and rear leaf elements 32,34. As an alternative, an opening with parallel sides, rather than a V-groove, can be used. In any event, it will be appreciated that when a wire is inserted in the V-grooves 30 of front and rear leaf elements 32,34, ears 36,38 separate. This effect is best seen in FIG. 4. As shown therein, as first wire 40 is inserted in V-groove 30, it spreads ears 36,38; they essentially bend as cantilevered beams. Thus, second wire 42 is not gripped securely when it is inserted. This can cause second wire 42 to be less securely retained than first wire 40. This effect is exacerbated by build up of insulation 44 which is sheared off of first wire 40 and then interferes with insulation 44 of second wire 42. Thus, there may not be room to fully receive second wire 42 into groove 30 due to interference from insulation 44. The interfering insulation and the spreading ears 36,38 which open up the V-groove 30 have made prior art insulation displacement contacts essentially unsuitable for use with two wires.
FIG. 5 depicts a prior art insulation displacement contact 24 secured in a prior art connector block contact holder 12. The insulation 44 of a wire 40 is secured by the strain relief elements 46 which define the narrow portions 20 of slot 16 (items 18 and 16 not labeled in drawing). It will be seen that both sides of insulation displacement contact 24 securely grasp the conductor of wire 40, however, it is also clear that there is no room for lateral displacement of insulation 44 and it will be substantially forced upward.
Reference should now be had to FIGS. 6A and 6B which are cross sections through the prior art connector block 10. In FIG. 6A, tails 26 of insulation displacement contacts 24 touch, and produce electrical contact between the two insulation displacement contacts 24. Contact is depicted by arrow 50. In FIG. 6B, tails 26 of contacts 24 are separated by a disconnect plug 48 formed from an insulating material. The separated contacts are indicated by arrow 52.
Reference should now be had to FIG. 7 which depicts a cross sectional plan view through a prior art contact holder 12 showing the insulation-displacement-contact-receiving cavity 22. The section is taken at a location where slots 16 have narrowed down to narrow part 20. It will be appreciated that cavity 22 includes a first pair of parallel walls 54 and a second pair of parallel walls 56 which are perpendicular to first pair of parallel walls 54. With continued reference to FIG. 7, and referring also back to FIG. 4, it will be appreciated that by making contact 24 a close fit in contact receiving cavity 22, spreading of V-groove 30 can be somewhat reduced by having ears 36,38 bear against walls 56. However, some clearance is generally necessary to insert contact 24. Further, the close fit can do nothing to alleviate the previously-discussed problem of interfering insulation, and may even exacerbate it.
At least one prior art device is specifically directed to terminating two wires in a single insulation displacement contact. U.S. Pat. No. 4,220,390 to Cobaugh et al. discloses a contact with three generally parallel leaf elements; two of which are essentially adjacent and have staggered offset slots which result in tighter gripping of wires when two wires are inserted. However, the construction of this device makes it not well suited for use in the confined spaces typical in modern telephone connector blocks. U.S. Pat. No. 5,588,859 to Maurice discloses a hermaphrodite contact having offset slots which are not staggered, and with two parallel leaf elements with no gap therebetween. It is not specifically directed to use with two wires, and although it has minimal depth, its relatively large width makes it undesirable for confined spaces. U.S. Pat. No. 5,131,863 to Gerke et al. discloses a cutting/clamping contact featuring a single plate-like element which is oriented at 45.degree. to the wire with which contact is to be made. There is no specific adaptation for two wires. Contact integrity in the Gerke et al. device could potentially be compromised by any melting or other degradation of the plastic body.
U.S. Pat. No. 4,097,107 to Hawkins discloses an insulation displacement terminal with offset, dogleg slots which are sprung with respect to each other for secure retention of a single wire; however, once a single wire is inserted, the configuration changes such that a second wire cannot be inserted.
In view of the deficiencies of prior art devices, there is a need for a two wire termination connection strip which is simple to manufacture, and which can provide reliable termination of two wires. The device should be adaptable to existing systems. Furthermore, any spreading open of the device upon insertion of the first wire should be minimized, and preferably substantially eliminated. Yet further, adequate provision should be made to deal with displaced insulation.